Unless I am totally lost here.......Entirely possible!!!!

My 1996 XJS has a separate vacuum system. I believe the CC is controlled with a small vacuum pump that sucks on the bladder and holds the throttle position when the CC is engaged?

I could be wrong.....If, Please let me know immediately.

Thanks

Soiftball60/Paul

 

Had rain yesterday, and I don't have a garage. Will do the vacuum test tomorrow.

I believe you are right about the separate system. Why else would the cruise have it's own vacuum pump.


1 - vacuum pump
2 - dump valve
3 - bellows
6 - cruise control ecu

 

Confirmed.

When de-energized, you can blow and suck freely (ba-dum chshhhh)

When energized, it is blocked. No sucking or blowing allowed.

Thank you. Thank you, I will be here all of the week!

 

Thinking to be my last post regarding this matter.

I decided to test again (explaining how I did it.

Unit is mounted as an assembly in the vehicle.

1. Removed the hose coming out of the pump that leads to the three (3) way fitting. 1 hose from the pump, 1 hose to the bellows, 1 hose leading to the dump valve.
2. Sucked on the hose leading to the bellows. No suction! Placed my finger over the opposite fitting leading from the pump...No difference!
3. Puts 12V to the dump valve to see If I could close the loop. Sucked on the hose again...No difference!!
4. Put 12V to the pump...Pump runs but not suck much!! Tried pinching off various hoses while pump running to see if I could collapse the bellows a bit.....Nothing!

When I place finger tip over pump fitting with the pump running...it does not seem to have any vacuum!!

So do I have a valve that does not function and a pump that barely SUCKS!!!!

I stated in an earlier post that it seemed to me that when you engage the CC master switch....It’s like it wants to works but it wont engage?


I give up...not sure what to do at this point??

Softball60/Paul

 

I hate to revive this issue but..............

The CC still does not function.

I have replaced the master switch, speed control, CC Computer, Vacuum Pump.....

Fuses are all good speedometer works brake lights work.

I just received and placed a functioning vacuum pump to replace my original.

With Engine not running.....

1. Disconnected the Electrical plug that goes into the vacuum pump.
2. Applied 12V external power to the vacuum pump it seems to sound stronger than my original.
3. No suction action on the bellows
4. Disconnected the hose leading to the dump valve
5. Placed finger over the 3 position plastic valve port leading from the dump valve
6. Bellows begins to collapse due to vacuum.

Does this mean that either 1. the dump valve is no good?.......(when energized 12V it make a slight clicking sound)........(when removed from the vehicle I tapped it several times to see if something was stuck in side the valve.....began to hear sound like paint rattle can after you shake and ball comes loose).

or 2. The dump valve is not getting the signal ( Under normal CC operation) to close which would create the vacuum with the pump running?

This all started after tearing every out of the trunk while replacing the fuel pump.......I checked for loose Ground wire!!!!!!!!

The only thing not checked is the stop switch located above the brake pedal!!! TOOOO Old to be trying to get in to this space!!!!

Any Ideas before I close this thread FOREVER!!!

Softball60/Paul

 

Can you trace the dump valve connection to the brake switch?
Do you know if the resting state of the car opens the valve?
Has the brake switch been checked for continuity?
I don't know if the any of switches are normally open or closed.
Keep up the good work and don't give in.

 

1. The dump valve runs to the Cruise Control module.
2. I don’t know if the valve is open at resting stage
3. The brake switch has not been checked....( It will be a challenge if I decide to do)......I will probably check at some point.....Hate to pay someone to do what I should be able to do.